1. Field of the Invention
The present invention relates to an image display apparatus and an image pickup apparatus equipped with the same. The present invention is suitable, for example, in the case where a two dimensional image is displayed on a predetermined surface using scanning means (which will also be called as light beam scanning means) for raster scanning a predetermined surface two-dimensionally with a light beam optically modulated based on image/video information emitted from light source means to make an image on the predetermined surface viewable.
2. Related Background Art
In image display apparatuses such as electronic viewfinder systems used in digital cameras, video cameras or the like, a two-dimensional type display element such as a transmission type liquid crystal or a reflection type liquid crystal is used in combination with an ocular system to allow a viewer to view an image formed and displayed on the two-dimensional type display element as a virtual image through an ocular system.
In recent years, the above-mentioned types of image display apparatuses are required to display images with higher definition. To meet such a requirement, in the case of the above-mentioned two-dimensional type display element, it is needed to produce pixels of a required pixel number on the display element. This presents the problem that pixel defects increase with an increase in the pixel number and the problem that manufacturing of the two-dimensional type display element is difficult since the size of each pixel is small relative to the size of the device. Furthermore, the two-dimensional type display element using liquid crystal suffers from after images that are generated when motion images are displayed, since the response speed of liquid crystal is low.
Still further, when image/video information formed by a two-dimensional type display element such as a liquid crystal display element is viewed, the pixel structure of the liquid crystal is sometimes recognizable.
There is a known image display apparatus in which the pixel structure is made invisible to thereby achieve excellent view by preventing deterioration of the quality of images as viewed (see Japanese Patent Application Laid-Open Nos. H06-130378 and H05-307174).
According to the method disclosed in Japanese Patent Application Laid-Open Nos. H06-130378 and H05-307174, to make the pixel structure of a liquid crystal display unrecognizable, an optical element having a microstructure is disposed in the viewing optical system (an ocular system) used in viewing an image displayed on the liquid crystal display, thereby making the pixel structure invisible.
A scanning type image display apparatus is also known (see U.S. Pat. No. 5,467,104). In the scanning type image display apparatus, instead of using a two-dimensional type display element, a surface to be scanned is scanned with a light beam modulated based on image/video information and emitted from light source means using light beam scanning means that is capable of two-dimensionally scanning to display an image that is viewed by a viewer. U.S. Pat. No. 5,467,104 discloses a technique in which red, blue and green light beams are two-dimensionally scanned in the horizontal and vertical directions and a two-dimensional image is directly formed on the retina of a viewer's eye by means of an optical system.
Characteristically, such an image display technique does not suffer from pixel defects in principle, since it is not necessary to use a display element on which pixels corresponding to required resolution are formed, unlike with the case of the image display apparatus that uses a two-dimensional image display element.
As a system that realizes such a scanning type image display apparatus, a micro electro mechanical system, which will be referred to as MEMS technology manufactured through a semiconductor process is known for use as light beam scanning means (see for example U.S. Pat. No. 5,606,447 and Japanese Patent Application Laid-Open No. H08-334723). The light beam scanning means manufactured based on MEMS technology is suitable for image display apparatuses, since they are small in size and light in weight and can operate at high speed. A MEMS technology serving as two-dimensional scanning means that can effect two-dimensional scanning for use in an image display apparatus for a head mount display apparatus has been known (see for example, Wafer Scale Packaging for a MEMS Video Scanner, SPIE Conference # 4407, 19 (June 2001)). The light beam scanning means based on the MEMS technology mechanically causes resonant motion of a light reflection surface using a torsion bar or the like to incline the light reflection surface utilizing torsion generated at that time, thereby deflecting and scanning a light beam incident on the reflection surface. Since torsion is utilized, the light reflection surface is not rotated but oscillated.
The basic frequency of such mechanical resonant motion is determined by the mechanical dimensions of the light beam scanning means. In addition, the light beam scanning means is attached with an actuator that generates an electrostatic force or an electromagnetic force, and the light beam scanning means is driven by the force generated by it in a resonant manner. According to the technology disclosed in the above mentioned U.S. Pat. No. 5,467,104, such a resonance type light beam scanning means is used for scanning in a first direction, and light beam scanning means for scanning a light beam in a second direction that is different from the first direction is further provided to realize two-dimensional scanning.
The light beam scanning means in a scanning type image display apparatus that utilizes resonance is adapted to perform scanning in a first direction as reciprocate motion, and to perform further scanning in a second direction that is perpendicular to the first direction to realize two-dimensional scanning. In this case, when resonant (oscilaring) reciprocate scanning in the first direction is performed, spaces between scanning lines become wider at the scanning ends in the first scanning direction in each scanning cycle. This makes the spaces between the scanning lines easily recognizable to the viewer, which leads to disadvantageous deterioration in the quality of the image viewed.
As a method for reducing the space between the scanning lines, the resonance frequency may be made higher to make the scanning lines dense. However, this method requires scanning means having high performance that realizes high speed scanning with high accuracy. This requires a complex structure.
Japanese Patent Application Laid-Open Nos. 06-130378 and 05-307174 teach to provide an optical element having a microstructure such as a micro prism or a diffraction grating, in a viewing optical system (or an ocular system) in order to prevent the pixel structure of a liquid crystal display from being recognized when image/video information formed by a two-dimensional display element such as a liquid crystal display is viewed. However, Japanese Patent Application Laid-Open Nos. 06-130378 and 05-307174 are directed to a structure that makes the pixel structure of liquid crystal as display means invisible. In addition, the technologies disclosed in Japanese Patent Application Laid-Open Nos. H06-130378 and H05-307174 are directed to liquid crystal display elements, which suffer from deterioration in the quality of images as viewed due to pixel defects and slowness in the response speed that is not necessarily sufficient for displaying motion pictures.
On the other hand, in the case where images are formed by an light scanning type image display apparatus for view, no technique for preventing spaces between scanning lines on a surface to be scanned (a surface to be viewed) from being recognized has not been proposed so far.
The method of using a micro structure in making the pixel structure of a two-dimensional display element such as a liquid crystal display unrecognizable disclosed in Japanese Patent Application Laid-Open Nos. 06-130378 and 05-307174 can not be applied to a light scanning type image display apparatus without modifications.